In gas turbines, a plurality of combustors are conventionally disposed in an annular array about the axis of the machine. Hot gases of combustion flow from each combustor through a transition piece into the first-stage nozzle. Because the transition pieces and the first-stage nozzle are formed of different materials and are subjected to different temperatures during operation, they experience different degrees of thermal growth. That is, both the transition pieces and the first-stage nozzle support elements move radially, circumferentially and axially relative to one another as a result of thermal growth. Also, similar relative movement occurs as a result of the dynamic pulsing of the combustion process. Thus, the time-variable mismatch at the junction of the transition pieces and the first-stage nozzle support elements, as a result of the thermal growth and dynamic spacing of these elements, requires an effective seal to contain the combustion products and the pressure differential across this space, while accommodating these dimensional changes in the radial, circumferential and axial directions.
Prior seals between transition pieces and first-stage nozzle elements typically have included relative rigid angled brackets for the top and bottom of the first-stage nozzle and a block of grooved metal that has lips that mesh with the corresponding grooves in each transition piece or the first-stage nozzle. Relative motion and thermal growth between the transition pieces and the first-stage nozzle are accommodated by the free movement of these parts, although such movement is limited by the lip-and-groove arrangement. Excessive wear of the mating parts in this type of seal occurs and necessitates undesirable frequent inspection intervals and shutdown for replacement.
Brush seals have been utilized in many environments in the past, usually between a stationary part and a rotating element. In U.S. Pat. No. 4,781,388, however, there is disclosed a brash seal for use in a gas turbine for sealing between relatively stationary parts and to accommodate dimensional differences caused by thermal growth and the dynamics of the system. However, the disclosed brash seals require a receiving element in the form of a fork for confining the distal ends of the bristles. Moreover, they are not used in sealing the space between combustion transition pieces and first-stage nozzles.